Has Barack Obama already caught a terminal case of the second-term curse? Still too early to diagnose.

But such an affliction will inevitably suffocate all his remaining legislative aspirations. The evidence from the past four decades leads to an unavoidable prognosis: The man’s got a little more than a year left, at most.

Each of the four previous re-elected presidents saw their juice on Capitol Hill run out well before their second-term congressional midterms. And there’s no empirical reason to believe that Obama will be able to make his political capital last any longer in this divided and divisive Congress.

Richard M. Nixon was able to keep alive his top priorities, which were about taking more power for himself at the expense of Congress, for only four months in 1973. Then the Senate Watergate Committee convened, galvanizing the nation’s interest in what the president knew and how long he’d known it.

Ronald Reagan decided to make a tax code overhaul the top domestic priority of his second term in May 1985, and he was able to revel in the climatic votes a year later. After that, the Iran-Contra scandal is all the historians have to say about the remainder of his presidency.

Bill Clinton pushed a landmark, bipartisan agreement on plans for balancing the federal budget through Congress in August 1997 and got to work on a typically disparate collection of other priorities. Traction for virtually all of them disappeared for good the following January, after the nation learned Monica Lewinsky’s name.

George W. Bush was about to see his choice elevated to chief justice of the United States on Labor Day 2005, and there was still a fighting chance Congress would permit his top second-term wish of getting some Social Security savings invested in the markets. His political capital evaporated immediately thereafter, when fury at his arms-length response to Hurricane Katrina combined with imploding support for the Iraq War.

For Obama, the lessons of his recent two-term predecessors is this: Even if he succeeds in weathering the current scandalous-sounding triple whammy — the IRS targeting of conservative groups, the seizing of journalists’ phone records, the shifting story about the Libya consulate attack — the president will be in the clear no longer than Election Day 2014. By then his legislative goals will have either been met or sidetracked for the duration.

His political opponents will make sure of it, one way or another.

Maybe they will tiptoe past the point of no return in pursuing a controversy, the way the Watergate investigations progressed, because plenty of lawmakers in both parties were willing to disbelieve as long as possible that their president was a criminal conspirator.

Maybe they’ll launch a formalized bipartisan court of inquiry, a la the Iran-Contra hearings, the path Democrats who ran the 100th Congress chose for marginalizing a still personally popular president.

Maybe the zealous umbrage and take-no-prisoners partisanship of a few Republicans will trump the cooler heads of the rest, the way Tom DeLay and his acolytes forced their way past the conventional wisdom that lying about sex with an intern was not the sort of “high crime” that drafters of the Impeachment Clause had in mind.

In each of those cases, the party that wasn’t running the White House came up with a way to turn one scandal into their best leverage for neutralizing whatever mandate could be claimed from the previous presidential election.

That’s not what happened four years ago. The most prominent scandal then — the case of the covert CIA agent exposed by White House officials as payback for her diplomat husband’s apostasy on Iraq — was certainly seamy. But no one ever talked seriously about impeaching Bush for it.

Instead, the Democratic minority decided its best approach was to turn its collective back on almost everything the president asked for, betting the voters would respond to the gridlock by turning over to them the keys to both the House and Senate in 2006.

It worked just as planned. That’s why the best wager at the moment is that Republicans will start emulating that approach very soon, assuming it can’t help but cement the universal expectation that they’ll hold the House and make a strong run at taking back the Senate next year.

Although an immigration overhaul remains the potential top-shelf exception, deficit curbs and gun control and the rest of Obama’s wishes will simply be left to wither. Instead, the GOP will seek to fill the air with a welter of oversight hearings on the three controversies of the moment, with some Democrats joining the outrage in the name of buying themselves political cover.

And the 2014 campaign will rumble into second gear as early as ever. For those of you not yet counting, the election is now 538 days away.